Double-rotor flux-switching machine

ABSTRACT

Advantageous machines, such as flux-switching machines (FSMs) are provided. An FSM can be yokeless and can have two rotors, which can be displaced from one another (e.g., by half a pole pitch). An FSM can be a flux-switching permanent magnet machine (FSPMM), and all magnets can be magnetized in the same circumferential direction. FSMs of the subject invention are cost-effective, have high torque density, and can operate well even under fault conditions.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 13/970,199, filed Aug. 19, 2013, which claims thebenefit of U.S. Provisional Application Ser. No. 61/684,853, filed Aug.20, 2012, which are hereby incorporated by reference herein in theirentireties, including any figures, tables, and drawings.

BACKGROUND

Electrical motors are used in a wide variety of applications, such asnaval vessels, aircrafts, washing machines, pumps, compressors, andhybrid vehicles. Advanced induction motors, permanent magnet motors, andhigh temperature superconducting motors are some examples that have beenidentified to be suitable for propulsion applications. Research hasrecently focused on permanent magnet motors as a basis for electricalpropulsion.

Flux-switching machines belong to the class of doubly-salient permanentmagnet (DPSM) machines but have not been traditionally used in theindustry. Instead, surface-mounted permanent magnet or interiorpermanent magnet machines have been used. Existing flux-switchingmachines show some disadvantages, including relatively low torquedensity compared to other permanent magnet machines.

BRIEF SUMMARY

The subject invention provides novel and advantageous machines, as wellas methods of manufacturing and using such machines. In manyembodiments, a machine can have a flux-switching topology and can be aflux-switching machine (FSM). Such machines can be used as, e.g., motorsand/or generators.

In one embodiment, an FSPMM includes a first rotor, a second rotor, anda stator disposed between the first rotor and the second rotor. Thestator includes at least two permanent magnets and a coil wrapped aroundeach permanent magnet, and the stator has a ring shape with an annularopening. All permanent magnets of the FSPMM are magnetized in the samecircumferential direction.

In a further embodiment, the stator, all permanent magnets, and allcoils are encapsulated in a non-magnetic encapsulating material.

In another embodiment, a method of manufacturing a flux-switchingpermanent magnet machine (FSPMM) includes: providing at least twopermanent magnets; providing a coil wound around each permanent magnet;providing the permanent magnets having coils wound around them within astator; and providing the stator between a first rotor and a secondrotor. The stator has a ring shape with an annular opening, and allpermanent magnets of the FSPMM are magnetized in the samecircumferential direction.

In a further embodiment, the method includes encapsulating the stator,the permanent magnets, and the coils in a non-magnetic encapsulatingmaterial, prior to providing the stator between the first rotor and thesecond rotor. The method can also include magnetizing the permanentmagnets such that all permanent magnets of the FSPMM are magnetized inthe same circumferential direction, wherein magnetizing the permanentmagnets is performed after encapsulating the stator, the permanentmagnets, and the coils in the non-magnetic encapsulating material.

In yet another embodiment, an FSM includes a first rotor, a secondrotor, and a stator disposed between the first rotor and the secondrotor, wherein the stator has a ring shape with an annular opening, andwherein the stator includes the features of a, the features of b, or thefeatures of c: a) at least two direct current (DC) field coils and aphase winding coil wrapped around each DC field coil; b) at least twohigh-temperature superconducting direct current (HTSCDC) field coils anda phase winding coil wrapped around each HTSCDC field coil; and c) atleast two DC field coil/permanent magnet hybrid combinations and a phasewinding coil wrapped around each DC field coil/permanent magnet hybridcombination, wherein each DC field coil/permanent magnet hybridcombination comprises a DC field coil, wherein all permanent magnets ofthe FSPMM are magnetized in the same circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Patent Office upon request andpayment of the necessary fee.

FIG. 1 is a cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 2 is a cross-sectional diagram showing open-circuit flux lines of amachine according to an embodiment of the subject invention.

FIG. 3 is an exploded perspective view of a machine according to anembodiment of the subject invention. End-connections of the statorwindings are not shown for clarity purposes.

FIG. 4 is cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 5 is cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 6 is cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 7 is a plot showing back-emf as a function of time.

FIG. 8 is a plot showing torque as a function of time.

FIG. 9 is a cross-sectional diagram showing the magnitude of the B fieldfor motor according to an embodiment of the subject invention.

FIG. 10 is a plot showing torque as a function of time.

FIG. 11 is a plot showing back-emf as a function of time.

FIG. 12 is a plot showing torque as a function of time.

FIG. 13 is a plot showing back-emf as a function of time.

FIG. 14 is cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 15 is cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 16 is cross-sectional diagram of a machine according to anembodiment of the subject invention.

FIG. 17 is perspective view of a machine according to an embodiment ofthe subject invention. End-connections of the stator windings are notshown for clarity purposes.

FIG. 18 is a cross-sectional diagram of a portion of a machine accordingto an embodiment of the subject invention.

DETAILED DISCLOSURE

When the term “about” is used herein, in conjunction with a numericalvalue, it is understood that the value can be in a range of 95% of thevalue to 105% of the value, i.e. the value can be +/−5% of the statedvalue. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.

When the terms “on” or “over” are used herein, when referring to layers,regions, patterns, or structures, it is understood that the layer,region, pattern, or structure can be directly on another layer orstructure, or intervening layers, regions, patterns, or structures mayalso be present. When the terms “under” or “below” are used herein, whenreferring to layers, regions, patterns, or structures, it is understoodthat the layer, region, pattern, or structure can be directly under theother layer or structure, or intervening layers, regions, patterns, orstructures may also be present.

In addition, references to “first”, “second”, and the like (e.g., firstand second portion), as used herein, and unless otherwise specificallystated, are intended to identify a particular feature of which there maybe more than one. Such reference to “first” does not imply that theremust be two or more. These references are not intended to confer anyorder in time, structural orientation, or sidedness (e.g., left orright) with respect to a particular feature, unless explicitly stated.

The terms “Conventional” and “Proposed” are used in some of the figures.These refer to embodiments of the subject invention (“Proposed”)compared with related art devices (“Conventional”).

The subject invention provides novel and advantageous machines, as wellas methods of manufacturing and using such machines. In manyembodiments, a machine of the subject invention is a double-rotor (DR)motor, such as a motor having a doubly-salient permanent magnet (PM)motor. In many embodiments, a motor can have a flux-switching topologyand can be a DR flux-switching machine or motor (FSM).

FSMs belong to the class of doubly-salient machines (DSM) and can havethe highest torque density of all DSM machines. Even though they havehigh torque density compared to other DSMs, FSMs were not traditionallypreferred as the performance was below that of other common PM machinessuch as a surface-mounted PM (SMPM) or interior PM (IPM) machine. Adistinct advantage of the FSMs of the subject invention, compared toSMPM and IPM machines, is that the PMs are not rotating. The rotatingpart can be made of, e.g., silicon steel (and can use no other materialsin certain embodiments) and is thus mechanically and thermally veryrugged. Flux-switching PM (FSPM) machines according to the subjectinvention overcome disadvantages of conventional FSPM machines and havea torque density that can almost match, or even surpass, SMPM and IPMmachines. For example, an FSPM machine according to the subjectinvention can have a torque density that is more than 40% higher thanthat of a conventional flux-switching machine.

In one embodiment of the subject invention, a machine can have adouble-rotor topology. A machine of the subject invention can have astator with coils (also referred to herein as “windings” and “phasewindings”) and/or one or more PMs. Such a machine can be configured suchthat the stator has an annular cross-section, with an outer rotorsurrounding it and an inner rotor within it. The outer rotor can have agenerally annular cross-section, and the inner rotor can have agenerally circular cross-section. Such a motor has several advantagesover existing motors, such as an SMPM. FSPMMs according to the subjectinvention can be considered doubly-salient rotary machines.

In embodiments of the subject invention, a machine can include two ormore PMs, and all PMs can be magnetized in the same direction (forexample, the same circumferential direction). Such a configuration isunique, as existing FSPM machines use oppositely-oriented magnets, andthis unique configuration of the subject invention provides improvedperformance.

In many embodiments, a machine (e.g., an FSPM machine) of the subjectinvention can have at least one magnet (e.g., at least one PM). Thenumber of magnets present in a machine of the subject invention can be,for example, any of the following values, at least any of the followingvalues, at most any of the following values, or within any range havingany of the following values as endpoints, though embodiments are notlimited thereto: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, 20, 25, 30, 35, 40, 45, 50, or 100. For example, the numberof magnets present in a machine of the subject invention can be 5, 6, or13.

FIG. 1 is a cross-sectional diagram showing the topology of an FSPMmachine (FSPMM) according to one embodiment of the subject invention.Referring to FIG. 1, an FSPMM can include one or more magnets 310, oneor more coils 330, an inner rotor 321, a stator 350, and an outer rotor325. In many embodiments, the magnets 310 are PMs, and an FSPMM includesat least two PMs 310. The FSPMM can be configured such that all PMs 310are magnetized in the same circumferential direction, as represented inFIG. 1 by the arrow on each magnet pointing in the same circumferentialdirection. The stator 350 can have an annular cross-section, with theouter rotor 325 surrounding it and the inner rotor 321 disposed withinit. That is, the stator 350 can have the shape of an annular cylinder ora ring (i.e., similar to the shape of a pipe, with the stator formingthe wall of the pipe). The outer rotor 325 can have a generally annularcross-section, with teeth 322 on an inner surface thereof facing thestator 350, and the inner rotor 321 can have a generally annularcross-section, with teeth 322 on an outer surface thereof facing thestator 350. The three-dimensional shape of the both the inner 321 andouter rotors 325 can be generally similar to that of the stator 350(i.e., a ring or a generally annular cylinder. Another structure, suchas a shaft, can be disposed within the inner rotor 321. In analternative embodiment, the inner rotor 321 can have a generallycylindrical shape, with no other structure disposed within it.

In many embodiments, the cross-section of both the outer surface of theouter rotor 325 and the inner surface of the outer rotor 325 (notincluding the teeth 322) is circular, and the cross-section of the outersurface of the inner rotor 321 (not including the teeth 322), as well asan inner surface of the inner rotor 321 (if present), is circular.

The machine shown in FIG. 1 is a 5-phase, 9-pole motor, thoughembodiments are not limited thereto; the machine shown in FIG. 1 is forexemplary purposes only. Though FIG. 1 shows five PMs for exemplarypurposes, embodiments are not limited thereto. Also, though FIG. 1 showsan inner rotor 321 and an outer rotor 325 for exemplary purposes,embodiments are not limited thereto. For example, a motor can have justone rotor 321, 325. Further, though FIG. 1 shows five phases (labeled A,B, C, D, and E) for exemplary purposes, embodiments are not limitedthereto.

The number of phases present in a machine of the subject invention canbe, for example, any of the following values, at least any of thefollowing values, at most any of the following values, or within anyrange having any of the following values as endpoints, thoughembodiments are not limited thereto: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, or 100. Forexample, the number of phases present in a machine of the subjectinvention can be 5, 6, or 13.

The number of slots present in a machine of the subject invention canbe, for example, any of the following values, at least any of thefollowing values, at most any of the following values, or within anyrange having any of the following values as endpoints, thoughembodiments are not limited thereto: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, or 100. Forexample, the number of slots present in a machine of the subjectinvention can be 5, 6, or 13.

The number of poles present in a machine of the subject invention canbe, for example, any of the following values, at least any of thefollowing values, at most any of the following values, or within anyrange having any of the following values as endpoints, thoughembodiments are not limited thereto: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, or 100. Forexample, the number of poles present in a machine of the subjectinvention can be 9, 10, or 17.

In an FSM of the subject invention, the following quantities can bedefined: r_(o) is the outer radius; r_(so) is the stator outer radius;r_(si) is the stator inner radius; r_(sh) is the shaft (if present)radius; L is the stack length; τ_(rp) is the rotor tooth pitch; w_(rt)it is the rotor tooth width; h_(rt) is the rotor tooth height; h_(rb) isthe rotor back-iron (if present) height; g is the air gap; w_(st) is thestator tooth width; and w_(m) is the magnet width. FIG. 18 shows across-sectional schematic of portion of an FSM indicating how thesequantities are measured. The 72° cut-out shown in FIG. 18 is forexemplary purposes; not all machines will have the same number ofmagnets, rotor teeth, rotor gaps, etc. within such a section. Also,though the airgaps between the inner rotor and the stator and betweenthe outer rotor and the stator are shown as equal, embodiments are notlimited thereto.

The outer radius (r_(o) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are in mm):0.01, 0.1, 1, 10, 50, 59, 100, 200, 300, 400, 500, or 1000. For example,the outer radius of a machine of the subject invention can be from10-500 mm.

The stator outer radius (r_(so) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are in mm):0.01, 0.1, 1, 8, 10, 48, 50, 100, 200, 300, 400, 498, 500, or 1000. Forexample, the stator outer radius of a machine of the subject inventioncan be from 8-498 mm.

The stator inner radius (r_(si) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are in mm):0.01, 0.1, 1, 6, 10, 25, 50, 100, 200, 300, 400, 496, 500, or 1000. Forexample, the stator inner radius of a machine of the subject inventioncan be from 6-496 mm.

The shaft radius (r_(sh) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are in mm):0.01, 0.1, 1, 10, 14, 50, 100, 200, 300, 400, 494, 500, or 1000. Forexample, the shaft radius of a machine of the subject invention can befrom 1-494 mm.

The stack length of a machine of the subject invention can be, forexample, any of the following values, at least any of the followingvalues, at most any of the following values, or within any range havingany of the following values as endpoints, though embodiments are notlimited thereto (all numerical values are in mm): 0.01, 0.1, 1, 5, 10,50, 100, 200, 300, 400, 500, 1000, 2000, 3000, 4000, 5000, or 10000. Forexample, the stack length of a machine of the subject invention can befrom 5-5000 mm.

The rotor tooth pitch (τ_(rp), in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are angles indegrees): 0.01, 0.1, 0.6, 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100,110, 120, 130, 140, 150, 160, 170, or 180. For example, the rotor toothpitch of a machine of the subject invention can be from 0.6 to 180degrees.

The rotor tooth width (w_(rt) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are angles indegrees): 0.01, 0.1, 0.5, 1, 5, 10, 20, 30, 40, 50, 60, 70, 75, 80, 90,100, 110, or 120. For example, the rotor tooth width of a machine of thesubject invention can be from 0.5 to 75 degrees.

The rotor tooth height (h_(rb) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are in mm):0.01, 0.1, 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 300,400, or 500. For example, the rotor tooth height of a machine of thesubject invention can be from 1-100 mm.

The rotor back-iron height (h_(rb) in FIG. 18) of a machine of thesubject invention can be, for example, any of the following values, atleast any of the following values, at most any of the following values,or within any range having any of the following values as endpoints,though embodiments are not limited thereto (all numerical values are inmm 0.01, 0.1, 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 300,400, or 500. For example, the rotor back-iron height of a machine of thesubject invention can be from 1-100 mm.

Each air gap (g in FIG. 18) of a machine of the subject invention canbe, for example, any of the following values, at least any of thefollowing values, at most any of the following values, or within anyrange having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are in mm):0.001, 0.01, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70,80, 90, or 100. For example, each air gap of a machine of the subjectinvention can be from 0.1-50 mm.

The stator tooth width (w_(st) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are angles indegrees): 0, 0.001, 0.01, 0.1, 0.5, 1, 5, 10, 20, 30, 40, 50, 60, 70,80, 85, 88, 90, 100, 110, 120, 130, 140, or 150. For example, the statortooth width of a machine of the subject invention can be from 0 to 88degrees.

The magnet width (w_(m) in FIG. 18) of a machine of the subjectinvention can be, for example, any of the following values, at least anyof the following values, at most any of the following values, or withinany range having any of the following values as endpoints, thoughembodiments are not limited thereto (all numerical values are angles indegrees): 0, 0.001, 0.01, 0.1, 0.5, 1, 5, 10, 20, 30, 40, 50, 60, 70,80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 175, or 180. Forexample, the magnet width of a machine of the subject invention can befrom 0.5 to 175 degrees.

In many embodiments, an FSPMM can have an inner rotor 321 and an outerrotor 325, and the two rotors can be displaced from each other. Thedisplacement can be by, e.g., half a pole-pitch, though embodiments arenot limited thereto. That is, the rotors can be configured such that theteeth 322 from the outer rotor 325 line up with the gaps 323 (formedbetween the teeth 322) of the inner rotor 321, and vice versa. Such aconfiguration is shown in FIG. 2. A displacement as described can helpmaintain symmetry for flux flow. In an alternative embodiment, the tworotors can be lined up such that the teeth 322 from the outer rotor 325line up with the teeth 322 of the inner rotor 321, and the gaps 323 ofthe outer rotor 325 line up with the gaps 323 of the inner rotor 321.

In many embodiments, one or more of the magnets 310 can have a coil 330wrapped around it. For example, each magnet 310 present can have a coil330 wrapped around it. The windings of the coil 330 can be concentrated.It is to be understood that the coil 330 does not have to be wrappeddirectly around the magnet 310, and in many cases will be wrapped arounda portion of the stator 350 such that the coil 330 wraps around themagnet 310 with the portion of the stator 350 disposed therebetween.

In many embodiments, an FSPMM can be yokeless. The term yokeless meansthat no yoke is present in the FSPMM; that is, the FSPMM is configuredto not have a yoke. For example, the FSPMM can be without a back-iron inthe stator. In certain embodiments, the stator components are heldtogether with a non-magnetic material (an “encapsulator”). Theencapsulator can be any suitable material known in the art, for example,aluminum or an epoxy. In a particular embodiment, the encapsulator isaluminum with a thermally conductive epoxy resin.

The double-rotor FSPMM of the subject invention is similar in certainrespects to the flux-switching linear machine described in U.S. patentapplication Ser. No. 13/734,404 (hereinafter referred to as “the '404application”), filed Jan. 4, 2013, which is hereby incorporated byreference in its entirety, including any figures, tables, and drawings.The double-rotor FSPMM is similar to a double-stator version of themachine described in the '404 application, with each stator foldedaround on itself to correspond to the inner and outer rotors of thesubject invention, and the mover folded around on itself to correspondto the stator of the subject invention. A key difference is that FSPMMsof the subject invention provide rotary motion while motors of the '404application provide linear actuation.

FIG. 2 shows open-circuit flux lines for the machine shown in FIG. 1.The machine of the subject invention can utilize the width of windingslots to focus the flux through stator teeth.

FIG. 3 shows an exploded perspective view of an FSPMM according to anembodiment of the subject invention. Referring to FIG. 3, the stator 350is pulled out of the rotors for illustrative purposes. The stator 350can have a very modular structure that can simplify the constructionprocess. Each module can be made of a material with high magneticpermeability (e.g., soft magnetic composites (SMC) or steel, such aslaminated silicon steel) with an embedded magnet 310 (e.g., a PM), andthe coil 330 can be wound around the material with the embedded magnet.Each phase of the machine can have one or more coils, and the coils canbe in series, though embodiments are not limited thereto. The number ofcoils multiplied by the number of phases determines the number ofmodules in the stator. Even with concentrated windings, the open-circuitback-emfs can be sinusoidal. The entire stator 350 can be enclosed in anon-magnetic material, such as epoxy resin or aluminum. The rotors 320,including the inner 321 and outer 325 rotors, can be made of a materialwith high magnetic permeability (e.g., SMC or steel, such as laminatedsteel). The rotors 320 can be placed such that they are half apole-pitch apart to ensure symmetry, though embodiments are not limitedthereto. That is, the teeth 322 of the inner rotor 321 can be alignedwith the gaps 323 of the outer rotor 325, and vice versa. A yokelessmotor is shown in FIG. 3, and all of the stator components (e.g.,magnets 310, coils 330, and stator material) can be encapsulated by anon-magnetic encapsulating material 360 (e.g., epoxy). The rotors 320are not encapsulated by the encapsulating material 360. In a particularembodiment, the encapsulator material can be a thermally conductiveepoxy resin (e.g., 50-3185 NC, available from Epoxies, etc.). Suchresins have tensile strengths of more than 8,000 psi and a shore-Dhardness of more than 94, which is sufficient for encapsulating atranslator of an FSPMM of the subject invention.

FIG. 4 is a cross-sectional diagram showing an FSPMM according to oneembodiment of the subject invention. All magnets 310 are magnetized inthe same circumferential direction. The motor shown in FIG. 4 is a5-phase, 8-pole motor, shown for exemplary purposes. Though FIG. 4 showsfive phases (labeled A, B, C, D, and E) and five magnets for exemplarypurposes, embodiments are not limited thereto. FIG. 5 shows an FSPMMaccording to an embodiment of the subject invention having a very highnumber of magnets and poles. The rotors are configured such that theyare half a pole-pitch apart; i.e., the teeth 322 of the inner rotor 321are aligned with the gaps 323 of the outer rotor 325, and vice versa.All magnets 310 are magnetized in the same circumferential direction.FIG. 6 shows an FSPMM according to an embodiment of the subjectinvention having 13 magnets, 13 phases, and 17 poles. All magnets 310are magnetized in the same circumferential direction. The rotors areconfigured such that they are half a pole-pitch apart; i.e., the teeth322 of the inner rotor 321 are aligned with the gaps 323 of the outerrotor 325, and vice versa.

Each magnet present in the machines of the subject invention can be madeof any suitable material known in the art. For example, magnets can bemade of neodymium ferrite boron (NdFeB) or aluminum nickel cobalt(AlNiCo), though embodiments are not limited thereto. In a specificembodiment, magnets can be made of NdFeB-30.

Each rotor present in the machines of the subject invention can be madeof any suitable material known in the art. For example, each rotor canbe made of SMC or steel, such as carbon steel or laminated carbon steel(e.g., laminated carbon steel 1010), though embodiments are not limitedthereto.

Each coil present in the machines of the subject invention can be madeof any suitable material known in the art. For example, coils can bemade of copper, though embodiments are not limited thereto.

In certain embodiments, a machine can include one or more shafts. Eachshaft present in the motors of the subject invention can be made of anysuitable material known in the art. For example, shafts can be made ofcold-rolled or hot-rolled steel (e.g., stainless steel), thoughembodiments are not limited thereto.

In one embodiment, an FSM can include direct current (DC) field coils inplace of magnets. FIG. 14 is a cross-sectional diagram showing an FSPMMhaving DC field coils instead of magnets. Referring to FIG. 14, an FSMcan include one or more DC field coils 470, one or more phase windings430, an inner rotor 421, a stator 450, and an outer rotor 425. The FSMcan include at least two DC field coils 470. The FSM can be configuredsuch that the positive-negative axis orientation of all DC field coils470 is in the same radial direction, though embodiments are not limitedthereto. For example, the DC field coils 470 can be arranged such thatthe negative and positive sides are lined up perpendicular to thecircumferential direction of motion and all coils 470 have the positiveside closer to the outer rotor 425 than it is to the inner rotor 421, asshown in FIG. 14, though embodiments are not limited thereto (e.g., theDC field coils 470 can be arranged such that all have the negative sidecloser to the outer rotor 425 than it is to the inner rotor 421). In analternative embodiment, the positive-negative axis orientation of the DCfield coils 470 are not necessarily in the same radial direction.

The stator 450 can have an annular cross-section, with the outer rotor425 surrounding it and the inner rotor 421 disposed within it. That is,the stator 450 can have the shape of an annular cylinder or a ring.

The outer rotor 425 can have a generally annular cross-section, withteeth 422 on an inner surface thereof facing the stator 450, and theinner rotor 421 can have a generally annular cross-section, with teeth422 on an outer surface thereof facing the stator 450. Thethree-dimensional shape of the both the inner 421 and outer rotors 425can be generally similar to that of the stator 450 (i.e., a ring or agenerally annular cylinder. Another structure, such as a shaft, can bedisposed within the inner rotor 421. In an alternative embodiment, theinner rotor 421 can have a generally cylindrical shape, with no otherstructure disposed within it. The cross-section of both the outersurface of the outer rotor 425 and the inner surface of the outer rotor425 (not including the teeth 422) is circular, and the cross-section ofthe outer surface of the inner rotor 421 (not including the teeth 422),as well as an inner surface of the inner rotor 421 (if present), iscircular.

The inner rotor 421 and the outer rotor 425 can be displaced from eachother. The displacement can be by, e.g., half a pole-pitch. That is, therotors can be configured such that the teeth 422 from the outer rotor425 line up with the gaps 423 (formed between the teeth 422) of theinner rotor 421, and vice versa. Such a configuration is shown in FIG.14. In an alternative embodiment, the two rotors can be lined up suchthat the teeth 422 from the outer rotor 425 line up with the teeth 422of the inner rotor 421, and the gaps 423 of the outer rotor 425 line upwith the gaps 423 of the inner rotor 421. Also, in a particularembodiment, each DC field coil 470 can have a phase winding 430 wrappedaround it. The phase windings 430 can be concentrated. The phase winding430 does not have to be wrapped directly around the DC field coil 470,and in many cases will be wrapped around a portion of the stator 450such that the phase winding 430 wraps around the DC field coil 470 withthe portion of the stator 450 disposed therebetween.

In another embodiment, an FSM can include direct current (DC) fieldcoils and magnets. The magnets can be disposed, for example, adjacent tothe DC field coils or between the negative and positive sides of the DCfield coils, though embodiments are not limited thereto. FIG. 15 is across-sectional diagram showing an FSM having DC field coils andmagnets. Referring to FIG. 15, an FSM can include one or more DC fieldcoils 570, one or more magnets 510, one or more phase windings 530, aninner rotor 521, a stator 550, and an outer rotor 525. The magnets 510can be PMs, and the FSM can include at least two PMs 510. The FSM can beconfigured such that all PMs 510 are magnetized in the samecircumferential direction, as represented in FIG. 15 by the arrow oneach magnet pointing in the same circumferential direction. The FSM caninclude at least two DC field coils 570. The FSM can be configured suchthat all DC field coils 570 are arranged the same way, thoughembodiments are not limited thereto. For example, the DC field coils 570can be arranged such that the negative and positive sides are lined upperpendicular to the circumferential direction of motion and all coils570 have the positive side closer to the outer rotor 525 than it is tothe inner rotor 521, as shown in FIG. 15, though embodiments are notlimited thereto (e.g., the DC field coils 570 can be arranged such thatall have the negative side closer to the outer rotor 525 than it is tothe inner rotor 521, or the DC field coils 570 can be arranged such thatsome have the negative side closer to the outer rotor 525 and othershave the negative side closer to the inner rotor 521). In an alternativeembodiment, the positive-negative axis orientation of the DC field coils570 are not necessarily in the same radial direction.

The stator 550 can have an annular cross-section, with the outer rotor525 surrounding it and the inner rotor 521 disposed within it. That is,the stator 550 can have the shape of an annular cylinder or a ring.

The outer rotor 525 can have a generally annular cross-section, withteeth 522 on an inner surface thereof facing the stator 550, and theinner rotor 521 can have a generally annular cross-section, with teeth522 on an outer surface thereof facing the stator 550. Thethree-dimensional shape of the both the inner 521 and outer rotors 525can be generally similar to that of the stator 550 (i.e., a ring or agenerally annular cylinder. Another structure, such as a shaft, can bedisposed within the inner rotor 521. In an alternative embodiment, theinner rotor 521 can have a generally cylindrical shape, with no otherstructure disposed within it. The cross-section of both the outersurface of the outer rotor 525 and the inner surface of the outer rotor525 (not including the teeth 522) is circular, and the cross-section ofthe outer surface of the inner rotor 521 (not including the teeth 522),as well as an inner surface of the inner rotor 521 (if present), iscircular.

The inner rotor 521 and the outer rotor 525 can be displaced from eachother. The displacement can be by, e.g., half a pole-pitch. That is, therotors can be configured such that the teeth 522 from the outer rotor525 line up with the gaps 523 (formed between the teeth 522) of theinner rotor 521, and vice versa. Such a configuration is shown in FIG.14. In an alternative embodiment, the two rotors can be lined up suchthat the teeth 522 from the outer rotor 525 line up with the teeth 522of the inner rotor 521, and the gaps 523 of the outer rotor 525 line upwith the gaps 523 of the inner rotor 521. Also, in a particularembodiment, each DC field coil 570/magnet 510 combination can have aphase winding 530 wrapped around it. The phase windings 530 can beconcentrated. The phase winding 530 does not have to be wrapped directlyaround the DC field coil 570/magnet 510 combination, and in many caseswill be wrapped around a portion of the stator 550 such that the phasewinding 530 wraps around the DC field coil 570/magnet 510 combinationwith the portion of the stator 550 disposed therebetween.

In yet another embodiment, an FSM can include high-temperaturesuperconducting direct current (HTSCDC) field coils in place of magnets.FIG. 16 is a cross-sectional diagram showing an FSM having HTSCDC fieldcoils instead of magnets. Referring to FIG. 16, an FSM can include oneor more HTSCDC field coils 680, one or more phase windings 630, an innerrotor 621, a stator 650, and an outer rotor 625. The FSM can include atleast two HTSCDC field coils 680. The FSM can be configured such thatall HTSCDC field coils 680 are arranged the same way, though embodimentsare not limited thereto. For example, the HTSCDC field coils 680 can bearranged such that the negative and positive sides are lined upperpendicular to the circumferential direction of motion and all coils680 have the positive side closer to the outer rotor 625 than it is tothe inner rotor 621, as shown in FIG. 16, though embodiments are notlimited thereto (e.g., the HTSCDC field coils 680 can be arranged suchthat all have the negative side closer to the outer rotor 625 than it isto the inner rotor 621). In an alternative embodiment, thepositive-negative axis orientation of the HTSCDC field coils 670 are notnecessarily in the same radial direction.

The stator 650 can have an annular cross-section, with the outer rotor625 surrounding it and the inner rotor 621 disposed within it. That is,the stator 650 can have the shape of an annular cylinder or a ring.

The outer rotor 625 can have a generally annular cross-section, withteeth 622 on an inner surface thereof facing the stator 650, and theinner rotor 621 can have a generally annular cross-section, with teeth622 on an outer surface thereof facing the stator 650. Thethree-dimensional shape of the both the inner 621 and outer rotors 625can be generally similar to that of the stator 650 (i.e., a ring or agenerally annular cylinder. Another structure, such as a shaft, can bedisposed within the inner rotor 621. In an alternative embodiment, theinner rotor 621 can have a generally cylindrical shape, with no otherstructure disposed within it. The cross-section of both the outersurface of the outer rotor 625 and the inner surface of the outer rotor625 (not including the teeth 622) is circular, and the cross-section ofthe outer surface of the inner rotor 621 (not including the teeth 622),as well as an inner surface of the inner rotor 621 (if present), iscircular.

The inner rotor 621 and the outer rotor 625 can be displaced from eachother. The displacement can be by, e.g., half a pole-pitch. That is, therotors can be configured such that the teeth 622 from the outer rotor625 line up with the gaps 623 (formed between the teeth 622) of theinner rotor 621, and vice versa. Such a configuration is shown in FIG.16. In an alternative embodiment, the two rotors can be lined up suchthat the teeth 622 from the outer rotor 625 line up with the teeth 622of the inner rotor 621, and the gaps 623 of the outer rotor 625 line upwith the gaps 623 of the inner rotor 621. Also, in a particularembodiment, each HTSCDC field coil 680 can have a phase winding 630wrapped around it. The phase windings 630 can be concentrated. The phasewinding 630 does not have to be wrapped directly around the HTSCDC fieldcoil 670, and in many cases will be wrapped around a portion of thestator 650 such that the phase winding 630 wraps around the HTSCDC DCfield coil 670 with the portion of the stator 650 disposed therebetween.

In yet another embodiment, an FSM can include field coils and magnets,as shown in FIG. 15 and as discussed above with reference to FIG. 15,but the field coils can be HTSCDC field coils.

In yet another embodiment, an FSM can have an axial arrangement of therotors and the stator instead of a rotary arrangement. FIG. 17 is across-sectional diagram showing an axial FSM. Referring to FIG. 17, anaxial FSM can include one or more magnets 710, one or more coils 730, afirst rotor 721, a stator 750, and a second rotor 725. The magnets 710can be PMs, and the FSM can include at least two PMs 710. The FSM can beconfigured such that all PMs 710 are magnetized in the samecircumferential direction. The stator 750 can have an annularcross-section, such that the stator 750 can have the shape of an annularcylinder or a ring. The first 721 rotor can have a generally annularcross-section, with teeth 722 on an upper surface thereof facing thestator 750, and the second rotor 725 can have a generally annularcross-section, with teeth 722 on a lower surface thereof facing thestator 750. The three-dimensional shape of both the first 721 and second725 rotors can be generally similar to that of the stator 750 (i.e., aring or a generally annular cylinder). Though FIG. 17 depicts a hole inthe center of the rotors 721, 725 and the stator 750, embodiments arenot limited thereto. One or more of the first rotor 721, the secondrotor 725, and the stator 750 can be solid all the way through (giving acylindrical or disc shape) and/or one or more of these structures canhave another structure (e.g., a shaft) filling in the hole.

The first rotor 721 and the second rotor 725 can be displaced from eachother. The displacement can be by, e.g., half a pole-pitch. That is, therotors can be configured such that the teeth 722 from the first rotor721 line up with the gaps 723 (formed between the teeth 722) of thesecond rotor 725, and vice versa. Such a configuration is shown in FIG.17. Also, in a particular embodiment, each magnet 710 can have a phasewinding 730 wrapped around it. The phase windings 730 can beconcentrated. The phase winding 730 does not have to be wrapped directlyaround the magnet 710, and in many cases will be wrapped around aportion of the stator 750 such that the phase winding 730 wraps aroundthe magnet 710 with the portion of the stator 750 disposed therebetween.

In further embodiments, the axial structure shown in FIG. 17 can bemodified by: replacing the magnets with DC field coils (similar to theembodiment shown in FIG. 14, but with the axial structure); using DCfield coils in addition to magnets (similar to the embodiment shown inFIG. 15, but with the axial structure); replacing the magnets withHTSCDC field coils (similar to the embodiment shown in FIG. 14, but withthe axial structure); using HTSCDC field coils in addition to magnets(similar to the embodiment shown in FIG. 15, but with the axialstructure and with HTSCDC field coils instead of the DC coils 570).

In one embodiment, a method of manufacturing an FSM includes providingat least two permanent magnets, providing a coil wound around eachpermanent magnet, providing the permanent magnets having coils woundwithin a stator having an annular cross-section, and providing thestator between an outer rotor and an inner rotor. The order in which therotors are provided does not matter; i.e., the inner rotor can beprovided within the stator before the outer rotor is provided around thestator, or vice versa. The rotors can be provided such that they aredisplaced from each other. The displacement can be by half a pole pitch,i.e., such that the rotor teeth of the inner rotor are aligned with theteeth gaps between the rotor teeth of the outer rotor and vice versa,though embodiments are not limited thereto.

In a further embodiment, the method includes encapsulating the stator,the magnets, and the coils in a non-magnetic material (as discussedherein) before providing them between the rotors.

In yet a further embodiment, the method includes magnetizing the magnetssuch that all magnets are magnetized in the same circumferentialdirection. In a particular embodiment, the magnets can be magnetizedafter coils are wound around the magnets, after the magnets and coilsare provided within the stator, or even after the stator is providedbetween the inner and outer rotors. That is, the magnets can bemagnetized externally.

In further embodiments, the method can include forming the magnets,forming the coils, forming the stator, and/or forming the rotors.

In yet further embodiments, the steps involving the magnets can bereplaced with DC field coils or HTSCDC field coils, or the stepsinvolving the magnets can be supplemented with providing DC field coilsor HTSCDC field coils and then performing each step performed on themagnets on the DC field coils or HTSCDC field coils as well.

In another embodiment, a method of manufacturing an axial FSM includesproviding at least two permanent magnets, providing the permanentmagnets within a stator having an annular cross-section, providing acoil wound around each permanent magnet (each coil can be wound around aportion of the stator with the stator within it), and providing thestator axially between a first rotor and a second rotor (e.g., in themanner shown in FIG. 17). The order in which the rotors are provideddoes not matter; i.e., the first rotor can be provided on one side ofthe stator before the outer rotor is provided on the other side of thestator, or vice versa. The rotors can be provided such that they aredisplaced from each other. The displacement can be by, e.g., half a polepitch (i.e., such that the rotor teeth of the first rotor are alignedwith the teeth gaps between the rotor teeth of the second rotor and viceversa).

In a further embodiment, the method of manufacturing an axial FSMincludes encapsulating the stator, the magnets, and the coils in anon-magnetic material (as discussed herein) before providing thembetween the rotors.

In yet a further embodiment, the method of manufacturing an axial FSMincludes magnetizing the magnets such that all magnets are magnetized inthe same circumferential direction. In a particular embodiment, themagnets can be magnetized after coils are wound around the magnets,after the magnets and coils are provided within the stator, or evenafter the stator is provided between the rotors. That is, the magnetscan be magnetized externally.

In further embodiments, the method of manufacturing an axial FSM caninclude forming the magnets, forming the coils, forming the stator,and/or forming the rotors.

In yet further embodiments, the steps (of the method of manufacturing anaxial FSM) involving the magnets can be replaced with DC field coils orHTSCDC field coils, or the steps involving the magnets can besupplemented with providing DC field coils or HTSCDC field coils andthen performing each step performed on the magnets on the DC field coilsor HTSCDC field coils as well.

In one embodiment, a method of using an FSM as described herein includesproviding an FSM as described herein and using it according to itsnormal functions. For example, an FSM can be used to provide rotarymovement.

FSMs according to embodiments of the subject invention have severaladvantages over existing motors. Flux-switching topology combines theadvantages of both switched reluctance machines and PM machines andthereby gives high torque density. The torque density is even higherthan surface-mounted PM machines or interior PM machines with the sameamount of magnet volume and active machine volume.

The use of a yokeless stator in embodiments of the subject inventionallows very good torque versus current linearity, which is highlybeneficial—for example, when overloading the machine due to emergencysituations.

The highly modular structure of the FSM allows it to operate withseveral different numbers of phases (e.g., 3, 5, 13, etc.). Withmultiple phases, the machine can be operated well even under faultconditions. The construction of the machine is easy due to the modularstructure.

Also, the cogging torque is very low (e.g., <1% of torque) for uniqueslot-pole combinations of the device. In addition, the motor can bemodified easily to have either sinusoidal or trapezoidal back-emfdepending on the application.

The saturation effect on the torque is very small in embodiments of thesubject invention due to the yokeless topology, and consequently, themachine can be controlled very easily to have very low torque rippleseven under fault conditions.

Further, there is little concern about demagnetizing the magnets as thefield due to PMs is perpendicular to the field due to currents in thewindings. Permanent magnets that are embedded in the stator are allmagnetized in the same circumferential direction. During construction ofthe machine, this is highly beneficial as the stator can be built first,and then magnetized externally. Also, cheaper magnets, such as AlNiComagnets, can be used without concerns about demagnetizing them.

In addition, in many embodiments, the magnets and the coils can bestationary. Only the rotors rotate, which makes the machine very robust.In an alternative embodiment, the rotors are stationary and the statorrotates in use.

The device is modular, easy to assemble, and can be easily controlled.The modular nature of the device allows it to be operated with multiplephases easily and can be designed to be highly fault-tolerant. From aperformance point of view, the device has very low torque ripples and ahigh torque density, making it a suitable choice for many high precisionapplications.

FSMs of the subject invention are advantageous in several applications,including, but not limited to, hybrid vehicles, electric ships (e.g.,naval and other marine vessels), aircrafts, washing machines,hydroelectric generators, wind generators, pumps, compressors, androbots.

A greater understanding of the present invention and of its manyadvantages may be had from the following examples, given by way ofillustration. The following examples are illustrative of some of themethods, applications, embodiments and variants of the presentinvention. They are, of course, not to be considered as limiting theinvention. Numerous changes and modifications can be made with respectto the invention.

Example 1

An FSPMM according to an embodiment of the subject invention wasproposed for use with advanced propulsion systems of large marinevessels (e.g., naval vessels). Back-emf and torque of the FSPMM wassimulated using finite-element analysis. The FSPMM of the subjectinvention used for analysis was a 13-phase, 13-slot/17-pole motor having13 PMs. A cross-sectional diagram of the FSPMM is shown in FIG. 6.

The FSPMM has an inner rotor 321 and an outer rotor 325; each rotor ismade of laminated silicon steel, and each has 17 teeth. The number ofteeth can determine the number of poles of the machine The stator ismodular and each module is made of laminated silicon steel with PMsembedded in it. Phase coils are wound around the silicon steel statormodule such that the current produces magnetic field that isperpendicular to the magnetic field of the PMs. The stator is yokeless(does not have any back iron). All PMs are magnetized in the samecircumferential direction. The rotors are arranged such that the toothof one rotor is displaced by half a tooth-pitch from the correspondingtooth on the other rotor. This ensures symmetry for flux flow. Bothrotors are connected to the same common shaft. The stator modules areheld together by a non-magnetic material.

FIG. 7 shows a plot of back-emf versus time for the FSPMM of the subjectinvention, and FIG. 8 shows a plot of torque versus time for the FSPMM.The FSPMM is designed for a 19 MW propulsion application, and theresults were simulated using finite-element analysis. These waveformswere obtained maintaining the motor speed at 150 rpm. Referring to FIG.7, the back-emf is almost sinusoidal. Better sinusoidal waveforms can beachieved through a complete optimization of the proposed FSPMM.

Referring to FIG. 8, the torque ripple is very low. It is less than 1%of the average torque and is highly desirable to maintain low mechanicalvibrations. This allows the air-gaps in the machine to be very small.

FIG. 9 shows a plot of the magnitude of B-field of the entire FSPMM whenit is operating at full load and rated speed. The FSPMM is designed suchthat the magnitude of B field in the stator and rotor is less than 2 Tin order to prevent saturation and excessive core losses.

Electrical motors form the core of advanced propulsion systems that areconsidered for naval vessels. A summary of motors that have beenconsidered for this application is provided in [1] and [2]. Advancedinduction motors, permanent magnet (PM) motors, and high temperaturesuperconducting motors can be suitable for propulsion applications.These motors have advantages and disadvantages discussed in [2], but PMmotors have the most advantages.

The FSPMM of the subject invention overcomes the disadvantages ofconventional FSPMMs and has a high torque density matchingsurface-mounted PM (SNPM) and interior PM (IPM) machines, which is morethan 40% higher than conventional flux-switching machines. The FSPMM ofthe subject invention is an excellent candidate for naval propulsion andother applications requiring high torque density. As the PMs are notrotating, it can be easier to cool them and thus, operate the machine ata much higher saturation level with easy thermal management.

Example 2

The FSPMM of Example 1 was compared with the advanced induction machine(AIM) as described in [3]. The AIM of [3] was developed by ALSTOM forthe U.S. Navy. While exact specifications for this machine areunavailable publicly, an estimate of the machine parameters is availablein [3]. Table 1 shows a comparison of the parameters of the FSPMM of thesubject invention (labeled “Proposed FSM” in Table 1) and the AIM of [3](labeled “Conventional” in Table 1). It can be seen that the statorouter diameter, stack length, air-gap, speed, and output power are keptconstant for the two machines for a fair comparison. All the parametersshown are only of the active machine. Volume and weight of the externalhousing, cooling assembly, and others are not included in thiscomparison.

TABLE 1 Comparison of FSPMM of the subject invention and AIM of [3]Parameter Conventional Proposed FSM Phases 15 13 Poles 12 17 Speed (rpm)150 150 Output Power (MW) 19 19.2 Current density (A/mm²) 3.5 2.8 Statorcooling Air Air Outer Diameter (m) 3.5 3.5 Stack length (m) 1.41 1.41Airgap length (mm) 8 8 (each airgap = 4) Total weight of active material51e3  42e3 (kg) Magnet weight (kg) NA 2.6e3 Power factor 0.85 0.92

The FSPMM of the subject invention weighs almost 9 tons less than theAIM does. The current density required is also less in the FSPMM. It isalso likely that the FSPMM has better efficiency than the AIM. This isbecause the major component of the losses (i.e., the copper loss) isreduced as the FSPMM replaces many of the conductors with PMs. Anotherpoint to note is the power factor of the FSPMM of the subject inventionis significantly higher than that of the AIM. This leads to less stresson the converters supplying power to the machine. The FSPMM of thesubject invention exhibits all the advantages of a PM-based motoragainst an induction motor, such as easy controllability,straightforward start and run at all load levels, and lower ripple. Inaddition, the FSPMM of the subject invention is different from other PMmachines because the PMs are not moving. Thermal management of the PMsis easier, and the machine can be operated at much higher capacitywithout concern for demagnetizing the PMs.

The FSPMM of the subject invention has significant advantages over theconventional AIM for propulsion applications. The same power output canbe achieved for a lower weight of the machine, while also giving betterefficiency and power factor. Additionally, thermal management of the PMsis easier, and the machine is more rugged as the moving part is onlysteel.

Example 3

An FSPMM according to an embodiment of the subject invention wascompared with a surface-mounted PM (SMPM) and an internal PM (IPM)machine for propulsion applications that require power levels of up to 6MW. Parameters of the SMPM and IPM machines were selected from [4], inwhich these two motors have been compared for marine applications. TheFSPMM of the subject invention used for analysis was a 5-phase,15-slot/18-pole motor having 15 PMs. The cross-sectional diagram of theFSPMM is similar to that shown in FIG. 6, but with a different number ofphases, slots, poles, rotor teeth, and PMs.

The FSPMM has an inner rotor and an outer rotor; each rotor is made oflaminated silicon steel, and each has 18 teeth. The stator is modularand each module is made of laminated silicon steel with PMs embedded init. Phase coils are wound around the silicon steel stator module suchthat the current produces magnetic field that is perpendicular to themagnetic field of the PMs. The stator is yokeless, and all PMs aremagnetized in the same circumferential direction. The rotors arearranged such that the tooth of one rotor is displaced by half atooth-pitch from the corresponding tooth on the other rotor. Both rotorsare connected to the same common shaft. The stator modules are heldtogether by a non-magnetic material.

Table 2 shows a comparison of the parameters of the 5-phase,15-slot/18-pole FSPMM of the subject invention (labeled “Proposed FSM”in Table 2) and the SMPM (labeled “Conventional A” in Table 2) and IPM(labeled “Conventional B” in Table 2) machines of [4]. The FSPMM of thesubject invention has significant advantages over both the SMPM and IPMmachines. For the same volume and space constraints and similarair-gaps, the proposed FSPMM has much higher torque density than bothSMPM machine and IPM machine. Five phases of the proposed FSPMM havebeen considered in order to provide fault-tolerance to the motor. Whilethe weight of the motors is not available in [4], knowledge from theprevious simulations for the 19 MW application implies that the weightof the FSPMM of the subject invention will be at a comparable level tothat of the SMPM motor and the IPM motor.

TABLE 2 Comparison of FSPMM of the subject invention, SMPM of [4], andIMP of [4] Parameter Conventional A Conventional B Proposed FSM OutputPower (MW) 6.8 6.75 7.5 Phases 3 3 5 Stator slots 120 96 15 Poles 16 818 Speed (rpm) 170 170 170 RMS current 806 876 806 Current density 4 5 4(A/mm²) Stator cooling Air Air Air Torque Density 56.6 48.3 62.6 OuterDiameter (m) 1.75 1.89 1.75 Stack length (m) 2.78 2.78 2.78 Overallvolume (m³) 6.7 7.9 6.7 Airgap length (mm) 6 4 6 (each airgap = 3)

Example 4

An FSPMM according to an embodiment of the subject invention wasproposed for use with wind turbines (e.g., as a generator for off-shorewind turbines). Back-emf and torque of the FSPMM was simulated usingfinite-element analysis. The FSPMM of the subject invention used foranalysis was a 5-phase, 45-slot/81-pole motor having 45 PMs. Across-sectional diagram of the FSPMM is shown in FIG. 5. The motor hasan air-gap length of 5 mm for each air-gap.

The FSPMM has an inner rotor 321 and an outer rotor 325; each rotor ismade of steel, and each has 81 teeth. The number of teeth can determinethe number of poles of the machine. The stator is modular and eachmodule is made of steel with PMs embedded in it. Phase coils are woundaround the steel stator module such that the current produces magneticfield that is perpendicular to the magnetic field of the PMs. The statoris yokeless, and all PMs are magnetized in the same circumferentialdirection. The rotors are arranged such that the tooth of one rotor isdisplaced by half a tooth-pitch from the corresponding tooth on theother rotor.

FIG. 10 shows a plot of back-emf versus time for the FSPMM, and FIG. 11shows a plot of torque versus time for the FSPMM. The FSPMM is designedfor a 3 MW generator application, and the results were simulated usingfinite-element analysis. These waveforms were obtained maintaining themotor speed at 15 rpm. Referring to FIG. 10, the back-emf is somewhatsinusoidal. Referring to FIG. 11, the torque ripple is low.

Example 5

The FSPMM of Example 4 was compared with a direct-drive PM synchronousmachine (PMSM). Table 3 shows a comparison of the parameters of theFSPMM of the subject invention (labeled “Proposed FSM” in Table 3) andthe direct-drive SMPM (labeled “direct-drive PMSM” in Table 3).

TABLE 3 Comparison of FSPMM of the subject invention and direct-drivePMSM Parameter Direct-Drive PMSM Proposed FSM Phases 3 5 Slots 480 45Poles 160 81 Speed (rpm) 15 15 Power (MW) 3 3 Outer Diameter (m) 5 4.5Stack length (m) 1.2 1.2 Airgap length (mm) 5 5 (each airgap) Magnetweight (kg) 1.7 1.7 Copper weight (ton) 4.3 8.7 Steel weight (ton) 18.119.5 Total weight (ton) 24.1 29.9

Example 6

An FSPMM according to an embodiment of the subject invention wasproposed for use with wind turbines (e.g., as a generator for off-shorewind turbines). Back-emf and torque of the FSPMM was simulated usingfinite-element analysis. The FSPMM of the subject invention used foranalysis was a 5-phase, 45-slot/81-pole motor having 45 PMs. Across-sectional diagram of the FSPMM is shown in FIG. 5. The motordiffers from that of Example 4 by having an air-gap length of 2.5 mm foreach air-gap.

The FSPMM has an inner rotor 321 and an outer rotor 325; each rotor ismade of steel, and each has 81 teeth. The stator is modular and eachmodule is made of steel with PMs embedded in it. Phase coils are woundaround the steel stator module such that the current produces magneticfield that is perpendicular to the magnetic field of the PMs. The statoris yokeless, and all PMs are magnetized in the same circumferentialdirection. The rotors are arranged such that the tooth of one rotor isdisplaced by half a tooth-pitch from the corresponding tooth on theother rotor.

FIG. 12 shows a plot of back-emf versus time for the FSPMM, and FIG. 13shows a plot of torque versus time for the FSPMM. The FSPMM is designedfor a 3 MW generator application, and the results were simulated usingfinite-element analysis. These waveforms were obtained maintaining themotor speed at 15 rpm. Referring to FIG. 12, the back-emf is somewhatsinusoidal. Referring to FIG. 13, the torque ripple is low.

Example 7

The FSPMM of Example 6 was compared with a direct-drive PM synchronousmachine (PMSM). Table 4 shows a comparison of the parameters of theFSPMM of the subject invention (labeled “Proposed FSM” in Table 4) andthe direct-drive SMPM (labeled “direct-drive PMSM” in Table 4).

TABLE 4 Comparison of FSPMM of the subject invention and direct-drivePMSM Parameter Direct-Drive PMSM Proposed FSM Phases 3 5 Slots 480 45Poles 160 81 Speed (rpm) 15 15 Power (MW) 3 3 Outer Diameter (m) 5 4.5Stack length (m) 1.2 1.2 Airgap length (mm) 5 2.5 (each airgap) Magnetweight (kg) 1.7 1.7 Copper weight (ton) 4.3 8.7 Steel weight (ton) 18.119.5 Total weight (ton) 24.1 29.9

Example 8

An FSPMM according to an embodiment of the subject invention wasproposed with an output power of 2 kilowatts (kW) or about 2 kW. Thedevice had magnets all magnetized in the same circumferential direction,and had the parameters shown in Table 5. For a device with higher orlower power, the parameters can be scaled accordingly.

TABLE 5 Parameters of FSPMM Parameter Symbol Value Outer radius r_(o) 59mm Stator outer radius r_(so) 48 mm Stator inner radius r_(si) 25 mmShaft radius r_(sb) 14 mm Stack length L 100 mm  Rotor tooth pitchτ_(rp) 40° Rotor tooth width w_(rt) 16° Rotor tooth height h_(rt)  5 mmRotor back-iron height h_(rb)  5 mm Airgap g  1 mm Stator tooth widthw_(st) 13.85°   PM width w_(m) 6.3° 

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. In addition, anyelements or limitations of any invention or embodiment thereof disclosedherein can be combined with any and/or all other elements or limitations(individually or in any combination) or any other invention orembodiment thereof disclosed herein, and all such combinations arecontemplated with the scope of the invention without limitation thereto.

Although the disclosed subject matter has been described and illustratedwith respect to embodiments thereof, it should be understood by thoseskilled in the art that features of the disclosed embodiments can becombined, rearranged, etc., to produce additional embodiments within thescope of the invention, and that various other changes, omissions, andadditions may be made therein and thereto, without parting from thespirit and scope of the present invention.

What is claimed is:
 1. A flux-switching permanent magnet machine(FSPMM), comprising: a first rotor; a second rotor; and a statordisposed between the first rotor and the second rotor, wherein thestator comprises a plurality of modules, each of the plurality ofmodules comprising a high magnetic permeability material having a firstend, a second end, a plurality of slots, a permanent magnet embeddedbetween the first and second ends, and at least one coil wrapped aroundthe permanent magnet at one or both of the first and second ends;wherein the stator has a ring shape with an annular openings; whereinall permanent magnets of the FSPMM are magnetized in the samecircumferential direction of the stators; wherein each coil that iswrapped around a permanent magnet is disposed in a slot of the pluralityof slots of the stator; wherein adjacent permanent magnets of the FSPMMare not connected via a yoke; wherein the plurality of modules arearranged end-to-end such that the at least one coil of a first module isadjacent to the at least one coil of a second module.
 2. The FSPMMaccording to claim 1, wherein the first rotor is disposed within theannular opening of the stator, wherein the second rotor has a ring shapewith an annular opening, and wherein the stator is disposed within theannular opening of the second rotor.
 3. The FSPMM according to claim 2,wherein the first rotor comprises rotor teeth on a surface thereoffacing the stator, wherein the first rotor comprises teeth gaps betweenthe rotor teeth of the first rotor, wherein the second rotor comprisesrotor teeth on a surface thereof facing the stator, wherein the secondrotor comprises teeth gaps between the rotor teeth of the second rotor,and wherein the first rotor and the second rotor are displaced from eachother by half a pole pitch such that the rotor teeth of the first rotorare aligned with the teeth gaps of the second rotor and the rotor teethof the second rotor are aligned with the teeth gaps of the first rotor.4. The FSPMM according to claim 1, wherein the stator comprises at leastfive permanent magnets, and wherein the number of phases of the FSPMM isat least three.
 5. The FSPMM according to claim 1, wherein the stator,all permanent magnets, and all coils are encapsulated in a non-magneticencapsulating material.
 6. The FSPMM according to claim 5, wherein thenon-magnetic encapsulating material comprises a thermally-conductingresin.
 7. The FSPMM according to claim 1, wherein each permanent magnetcomprises NdFeB or AlNiCo, wherein the stator comprises steel, whereinthe first rotor comprises steel, and wherein the second rotor comprisessteel.
 8. The FSPMM according to claim 1, wherein the first rotor has aring shape, wherein the second rotor has a ring shape, wherein the FSPMMhas an axial arrangement, such that neither the first rotor nor thesecond rotor is disposed within the annular opening of the stator, andwherein the first rotor is disposed on one side of the stator in theaxial direction and the second rotor is disposed on the other side ofthe stator in the axial direction.
 9. The FSPMM according to claim 8,wherein the first rotor comprises rotor teeth on a surface thereoffacing the stator, wherein the first rotor comprises teeth gaps betweenthe rotor teeth of the first rotor, wherein the second rotor comprisesrotor teeth on a surface thereof facing the stator, wherein the secondrotor comprises teeth gaps between the rotor teeth of the second rotor,and wherein the first rotor and the second rotor are displaced from eachother by half a pole pitch such that the rotor teeth of the first rotorare aligned with the teeth gaps of the second rotor and the rotor teethof the second rotor are aligned with the teeth gaps of the first rotor.10. The FSPMM according to claim 8, wherein the stator, all permanentmagnets, and all coils are encapsulated in a non-magnetic encapsulatingmaterial.
 11. The FSPMM according to claim 1, wherein each slot of theplurality of slots of the stator has a width configured to focus flux,from the permanent magnet around which the coil disposed in said slot iswrapped, across a first airgap separating the stator and the firstrotor, wherein the width of each slot is larger than the first airgap,wherein the first airgap is a shortest radial distance between thestator and the first rotor.
 12. The FSPMM according to claim 11, whereinthe width of each slot of the plurality of slots of the stator is alsoconfigured to focus flux, from the permanent magnet around which thecoil disposed in said slot is wrapped, across a second airgap separatingthe stator and the second rotor, wherein the second airgap is a shortestradial distance between the stator and the second rotor, and wherein asmallest width of each slot of the plurality of slots of the stator isgreater than both the first airgap and the second airgap.
 13. The FPSMMaccording to claim 12, wherein each coil is wrapped around itsrespective permanent magnet in a circumferential direction of thestator.
 14. A method of manufacturing a flux-switching permanent magnetmachine (FSPMM), comprising: providing a plurality of permanent magnets;providing the permanent magnets within a stator; providing a coil woundaround each permanent magnet; and providing the stator between a firstrotor and a second rotor, wherein the stator has a ring shape with anannular opening; wherein all permanent magnets of the FSPMM aremagnetized in the same circumferential direction of the stators; whereinthe stator comprises a plurality of modules, each of the plurality ofmodules comprising a high magnetic permeability material having a firstend, a second end, a plurality of slots, a permanent magnet embeddedbetween the first and second ends, and at least one coil wrapped aroundthe permanent magnet at one or both of the first and second ends;wherein each coil that is wrapped around a permanent magnet is disposedin a slot of the plurality of slots of the stators; wherein each coilfaces the first rotor and the second rotor; wherein adjacent permanentmagnets of the FSPMM are not connected via a yoke; wherein the pluralityof modules are arranged end-to-end such that the at least one coil of afirst module is adjacent to the at least one coil of a second module.15. The method according to claim 14, wherein the second rotor has aring shape with an annular opening, wherein providing the stator betweenthe first rotor and the second rotor comprises disposing the first rotorwithin the annular opening of the stator and disposing the stator withinthe annular opening of the second rotor, wherein the first rotor and thesecond rotor each comprises rotor teeth facing the stator and teeth gapsbetween the rotor teeth, and wherein the second rotor is provided suchthat it is displaced from the first rotor by half a pole pitch such thatthe rotor teeth of the first rotor are aligned with the teeth gaps ofthe second rotor and the rotor teeth of the second rotor are alignedwith the teeth gaps of the first rotor.
 16. The method according toclaim 14, further comprising: encapsulating the stator, the permanentmagnets, and the coils in a non-magnetic encapsulating material, priorto providing the stator between the first rotor and the second rotor,and magnetizing the permanent magnets such that all permanent magnets ofthe FSPMM are magnetized in the same circumferential direction of thestator, wherein magnetizing the permanent magnets is performed afterencapsulating the stator, the permanent magnets, and the coils in thenon-magnetic encapsulating material.
 17. The method according to claim14, wherein each slot of the plurality of slots of the stator has awidth configured to focus flux, from the permanent magnet around whichthe coil disposed in said slot is wrapped, across a first airgapseparating the stator and the first rotor, wherein the width of eachslot is larger than the first airgap, and wherein the first airgap is ashortest radial distance between the stator and the first rotor.
 18. Themethod according to claim 17, wherein the width of each slot of theplurality of slots of the stator is also configured to focus flux, fromthe permanent magnet around which the coil disposed in said slot iswrapped, across a second airgap separating the stator and the secondrotor, wherein the second airgap is a shortest radial distance betweenthe stator and the second rotor, and wherein a smallest width of eachslot of the plurality of slots of the stator is greater than both thefirst airgap and the second airgap.
 19. A flux-switching permanentmagnet machine (FSPMM), comprising: a first rotor; a second rotor; and astator disposed between the first rotor and the second rotor, whereinthe stator comprises a plurality of modules, each of the plurality ofmodules comprising a high magnetic permeability material having a firstend, a second end, a plurality of slots, a permanent magnet embeddedbetween the first and second ends, and at least one coil wrapped aroundthe permanent magnet at one or both of the first and second ends;wherein the plurality of modules are arranged end-to-end such that theat least one coil of a first module is adjacent to the at least one coilof a second module; wherein the stator has a ring shape with an annularopening; wherein all permanent magnets of the FSPMM are magnetized inthe same circumferential direction of the stator; wherein each coil thatis wrapped around a permanent magnet is disposed in a slot of theplurality of slots of the stator; wherein each coil directly faces thefirst rotor and the second rotor without a back-iron interposedtherebetween; wherein each slot of the plurality of slots of the statorhas a width configured to focus flux, from the permanent magnet aroundwhich the coil disposed in said slot is wrapped, across a first airgapseparating the stator and the first rotor; wherein the width of eachslot is larger than the first airgap; wherein the first airgap is ashortest radial distance between the stator and the first rotor; andwherein adjacent permanent magnets of the FSPMM are not connected via ayoke.
 20. The FSPMM according to claim 19, wherein the stator, allpermanent magnets, and all coils are encapsulated in a non-magneticencapsulating material.